<div dir="ltr"><div dir="ltr">On Sun, Sep 27, 2020 at 12:34 AM Ben Zaiboc via extropy-chat <<a href="mailto:extropy-chat@lists.extropy.org">extropy-chat@lists.extropy.org</a>> wrote:<br></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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On 27/09/2020 06:37, Adrian Tymes wrote:<br>
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<div dir="ltr">On Fri, Sep 25, 2020 at 11:38 AM Dave Sill via
extropy-chat <<a href="mailto:extropy-chat@lists.extropy.org" target="_blank">extropy-chat@lists.extropy.org</a>>
wrote:<br>
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<div dir="ltr">On Fri, Sep 25, 2020 at 12:50 PM Adrian
Tymes via extropy-chat <<a href="mailto:extropy-chat@lists.extropy.org" target="_blank">extropy-chat@lists.extropy.org</a>>
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<div dir="ltr">If these habitats are, say,
cylinders 2 km wide, to allow them to be spun up
to 1 G, that's enough of a technical (and
imposed-by-human-biology) standard that people
might not want to mess with it. 2 km wide
suggests maybe 5 km long maximum, for structural
stability.</div>
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<div>What about rotational stability? Wouldn't want
your habitats flipping when they're full of people.</div>
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<div><a href="https://www.youtube.com/watch?v=1VPfZ_XzisU" target="_blank">https://www.youtube.com/watch?v=1VPfZ_XzisU</a></div>
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<div>Per that video, you weight it so the axis of rotation
is not the one that's going to cause that sort of
flipping. </div>
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That would mean short, fat cylinders, not long thin ones, no?<br></div></blockquote><div><br></div><div>How short and fat, though? If 2 km wide by 5 km long is too long and thin...</div><div><br></div><div>2 km diameter is not the minimum for safe 1 G spin gravity (studies suggest 500 m, possibly smaller - see <a href="https://www.artificial-gravity.com/sw/SpinCalc/">https://www.artificial-gravity.com/sw/SpinCalc/</a> if you wish to play with the numbers). Wider is certainly possible. If 2x5 is enough for about 628K people, then 4x4 (so that length does not exceed width) should allow just over 2M.</div><div><br></div><div>The counterpoint, at least in the system I had been thinking of, is that the first habitat would start off only 100 meters - possibly only 10 meters - wide, since in its earliest days it would host less than 100 people for a while (less than 10 to start), and making far more habitat than necessary would be difficult to justify. 2x0.01 would still be enough for over 1,250 people; 4x0.01 could house over 5,000. If the eventual "objective" is to go to 4 km wide, there will be a stronger temptation to start off with just 500 km wide (0.5x0.01 is small enough that we're talking a single apartment building of about 31K square meters; even if we allocate 90% of the space to workshops, labs, agriculture, and open space, that's still right sized for about 100 people) - but once the initial radius is established, it will be far more difficult to expand the radius (which involves disrupting existing residential areas) than to simply extend the disc into a cylinder (which does not disrupt anyone's living situation). One could perhaps fully enclose the first cylinder within a wider second cylinder, but that presents a source of danger so long as the first cylinder spins much faster than the second within the second; the residents could be transitioned to the second cylinder once it's ready, and the first despun, but there will likely be resistance to "abandoning" the "historical" first colony structure. There will be even more resistance if the first cylinder is not within the second, as they will be seen as entirely different habitats. A much higher chance of long term success can be had by just starting at the radius it is desired to end up at.</div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div>It's interesting that we hadn't really understood this until
relatively recently. Makes me wonder what other physics we are still
completely in the dark about.<br></div></blockquote><div><br></div><div>My hunch is that the nature of dark matter/energy will become clearer once we have observatories scattered around the solar system (if not before then), and may well come down to the margin of error from Earth-only observations including results with strange consequences that will be ruled out by the greater precision such system-wide observation baselines will give.</div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div>I'm also wondering if a long thin cylinder flipping about a
perpendicular axis would be the disaster we are assuming (everything
inside being thrown about). What forces would the people inside
actually feel? Is it possible they wouldn't even notice unless they
were looking out of the window? Maybe it would be a cool quirk of
orbital habitats, and only be awkward for docking and astronomical
observations, rather than disastrous.</div></blockquote><div><br></div><div>No, it'd be brief but it would be significant turbulence for anyone inside. For spin gravity to work properly, the object providing spin gravity has to spin and experience no other motion. Any other motion is felt as other motion. </div></div></div>